Communication device comprising a carrier sense function and communication method

ABSTRACT

A communication device of an example of the present invention comprises a first unit determining that whether a state is a first state indicating that a transmission medium is in use, a second state indicating that the transmission medium is not in use, or a third state indicating that whether or not the transmission medium is in use is being determined, and a second unit prohibiting a data transmission in the first and third states, and permitting the data transmission in the second state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2008-191020, filed Jul. 24, 2008,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication device comprising acarrier sense function and a communication method.

2. Description of the Related Art

A wireless LAN communication conforming to the IEEE 802.11 standards(for example, IEEE 802.11a/b/g/n) executes a random access based oncarrier sense multiple access/with collision avoidance (CSMA/CA). Forthis reason, the arrival time of a received frame is unknown, andbasically, a terminal always executes a frame detection operation.

According to the wireless LAN communication, it is difficult to fullyavoid a frame error detection (i.e., a frame does not arrive;nevertheless, the frame arrival is detected) due to an influence of athermal noise of the self-station, or an electric noise of a peripheralapparatus.

According to the IEEE 802.11 standards, when a frame is detected, it isdetermined that a carrier exists, and transmission is prohibited and thevalue of a counter waiting a transmission opportunity is cleared. Forthis reason, the frame error detection is a major factor in losing atransmission opportunity.

For example, Reference 1 (Jpn. Pat. Appln. KOKAI Publication No.08-019030) discloses a technique of performing accurate carrier sensewithout receiving an influence of a noise generated by the device itselfbefore wireless transmission starts.

According to the technique disclosed in the Reference 1, when acommunication is executed, a control circuit operates a timer circuitfor fixed time and the control circuit itself is changed in a suspendedstate. When a time out is occurred by the timer circuit, an interruptionis executed for the control circuit, and the control circuit restarts.The control circuit executes a carrier sense using a wireless controllerafter it restarts. The Reference 1 discloses a technique that adetermination of clear channel assessment (CCA) is not executed in thetransmission timing because of a determination mistake being determinedthat a carrier exists though the carrier does not exist is oftenoccurred in the transmission timing.

In contrast, Reference 2 (Jpn. Pat. Appln. KOKAI Publication No.06-164444) discloses a technique that a CCA determination is notexecuted in the built-in DRAM refresh timing because of a determinationmistake being determined that a carrier exists though the carrier doesnot exist is often occurred in the built-in DRAM refresh timing.

However, according to the Reference 1 and 2, it is difficult to avoid anerror detection basis of a thermal noise and an unwanted radiationelectric wave except the self-station.

BRIEF SUMMARY OF THE INVENTION

According to first aspect of the invention, there is provided acommunication device comprising:

a first unit determining that whether a state is a first stateindicating that a transmission medium is in use, a second stateindicating that the transmission medium is not in use, or a third stateindicating that whether or not the transmission medium is in use isbeing determined; and

a second unit prohibiting a data transmission in the first and thirdstates, and permitting the data transmission in the second state.

According to second aspect of the invention, there is provided acommunication device comprising:

a receiving signal strength measuring unit measuring a strength of areceived signal;

a threshold determination unit determining whether or not the strengthof the received signal is equal to or more than a predeterminedthreshold value;

a receiving trigger unit issuing a data receiving start signal based onthe received signal;

a preamble detector unit determining whether or not a header of thereceived signal has a predetermined waveform after the data receivingstart signal is issued;

a receiving unit starting to receive the received signal after the datareceiving start signal is issued, and issuing a data receiving endsignal after a data receiving of the received signal ends,

a first carrier sense unit setting a first state indicating that atransmission medium is in use when it is determined that thetransmission medium is in use for the data receiving based on the datareceiving start signal and the data receiving end signal, and executinga transferring to a second state indicating that the transmission mediumis not in use when the threshold determination unit determines that thestrength of the received signal is not equal to or more than thepredetermined threshold value in the first state;

a second carrier sense unit executing a transferring to the first statewhen the threshold determination unit determines that the strength ofthe received signal is equal to or more than the predetermined thresholdvalue in the second state, and executing a transferring to a third stateindicating that whether or not the transmission medium is in use isbeing determined when the receiving trigger unit issues the datareceiving start signal in the second state;

a third carrier sense unit executing a transferring to the first statewhen the preamble detector unit determines that the header of thereceived signal has the predetermined waveform in the third state,executing a transferring to the second state when the preamble detectorunit determines that the header of the received signal does not have thepredetermined waveform in the third state, and executing a transferringto the first state when the threshold determination unit determines thatthe strength of the received signal is equal to or more than thepredetermined threshold value in the third state; and

a transmission unit transmitting data in the second state.

According to third aspect of the invention, there is provided a methodcomprising:

determining that whether a state is a first state indicating that atransmission medium is in use, a second state indicating that thetransmission medium is not in use, or a third state indicating thatwhether or not the transmission medium is in use is being determined;and

prohibiting a data transmission in the first and third states, andpermitting the data transmission in the second state.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram indicating an example of the configuration ofa communication device according to a first embodiment of the presentinvention.

FIG. 2 is a view to explain an example of the relationship between acount value of a counter, a busy state, an idle state and a pendingstate.

FIG. 3 is a block diagram indicating an example of the configuration ofa communication device according to a second embodiment of the presentinvention.

FIG. 4 is a view to explain an example of a state transition of acarrier sense unit according to the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be hereinafterdescribed with reference to the accompanying drawings. In the followingdrawings, the same numerals are used to designate identical portions,and the explanation is omitted.

First Embodiment

This first embodiment relates to a communication device comprising acarrier sense function. In the following description, system on a chip(SoC) employed for the IEEE 802.11 standards will be mainly explained. Asimilar technique as above is applicable to all of communication devicesexecuting a carrier sense.

This embodiment is a technique related to clear channel assessment (CCA)of wireless LAN communications (IEEE 802.11a/b/g/n, etc.). According tothis embodiment, a busy state (first state), an idle state (secondstate) and a pending state (third state), that is, a three-value CCA isemployed. Immediately after a received signal is detected, a statetransfers to the pending state, when it is confirmed that a detectionfor the received signal is not an error detection and the receivedsignal is a signal of wireless LAN communication, the state transfers tothe busy state. In the pending state, a frame transmission is stopped,but a value of a counter used for counting in an interval of acontinuous idle state is not cleared. In this way, it is possible toprevent a loss of a transmission opportunity due to frame errordetection such that a frame does not arrive; nevertheless, a framearrival is detected.

FIG. 1 is a block diagram indicating an example of the configuration ofa communication device according to a first embodiment of the presentinvention.

A communication device 1 determines whether or not a transmission mediumof a wireless LAN communication is in use (i.e., a received signal isbeing received and a transmission signal is being transmitted). Further,the communication device 1 includes a carrier sense unit 2, atransmission control unit 20 and a transmitter 4. The carrier sense unit2 determines any of a busy state, a pending state and an idle statebased on a result that whether or not the transmission medium is in useis determined.

The carrier sense unit 2 includes a use determination unit 5 and a statedetermination unit 6. The transmission control unit 20 includes acounter 3, a counter setting unit 7 and a transmission determinationunit 8.

The counter 3 is used for counting a time that the transmission mediumis not in use continuously (i.e., a free time of the transmissionmedium).

The use determination unit 5 determines whether or not the transmissionmedium is in use based on a received signal 101.

The state determination unit 6 determines whether a state is the busystate indicating that the transmission medium is in use, an idle stateindicating that the transmission medium is not in use (the transmissionmedium is free), and a pending state indicating that the communicationdevice 1 is on determination whether or not a transmission medium is inuse and temporarily pending based on a determined result by the usedetermination unit 5.

The counter setting unit 7 sets an initial value (predetermined value)for the counter 3 when the communication device 1 is in an initial stateand when the state determination unit 6 determines that the state is thebusy state. A timing of setting the initial value for the counter 3 maybe taken anytime between the other state transfers to the busy state andthe busy state transfers to another state.

The counter setting unit 7 outputs a count instruction signal 102 to thecounter 3 when the state determination unit 6 determines that the statetransfers from the busy state to the idle state. Hereby, an operation ofincrementing (count up) or decrementing (count down) of the counter 3 isstarted.

The counter setting unit 7 maintains the operation of incrementing ordecrementing of the counter 3 when the state determination unit 6determines that the state transfers from the idle state to the pendingstate.

The transmission determination unit 8 inputs a count value 103 which isoutputted from the counter 3, and then, determines that a datatransmission is possible when the state determination unit 6 determinesthat the state is the idle state and when the count value 103 of thecounter 3 is “equal to or more than” or “equal to or less than” apredetermined threshold. Further, the transmission determination unit 8outputs a transmission enabling signal 104 to the transmitter 4 when itis determined that the data transmission is possible. The transmissiondetermination unit 8 prohibits the data transmission when the statedetermination unit 6 determines that the state is the busy state and thepending state and when the state is the idle state and the count value103 of the counter 3 is not “equal to or more than” or “equal to or lessthan” the predetermined threshold.

When inputting a transmission request signal 105 and the transmissionenable signal 104 indicating that the transmission determination unit 8determines that the data transmission is possible, the transmitter 4outputs a transmission signal 106 and carries out the data transmission.

FIG. 2 is a view to explain of an example of the relationship betweenthe count value of the counter 3, the busy state, the idle state and thepending state.

The counter setting unit 7 of the transmission control unit 20 sets thecounter 3 so that the counter 3 has the initial value in the initialstate, after a frame is received (any time until a frame receiving endfrom a frame receiving start) and after a frame is transmitted (any timeuntil a frame transmission end from a frame transmission start) (t1).

The count value of the counter 3 is decremented in the idle state. Thetransmission determination unit 8 of the transmission control unit 20determines that the data transmission is possible when the count valueof the counter 3 becomes zero in an idle state I1 (t2). When thetransmission determination unit 8 determines that the data transmissionis possible, the transmitter 4 transmits a transmission frame if thetransmission frame is prepared. Then, the state determination unit 6 ofthe carrier sense unit 2 transfers the state from the idle state to abusy state B1.

In this case, the count value of the counter 3 is decremented. However,the count value of the counter 3 may be incremented. Specifically, whenthe count value reaches the predetermined value which is greater thanthe initial value in the idle state, the transmission determination unit8 determines that the transmission frame is transmittable. Thetransmission determination unit 8 of the transmission control unit 20determines that the transmission is possible when the count value of thecounter 3 becomes zero in the idle state. In this case, the transmissiondetermination unit 8 determines that the transmission is possible whenthe count value of the counter 3 becomes another predetermined valuewhich is less than the initial value in the idle state.

When the frame transmission ends (t3), the state determination units 6of the carrier sense unit 2 transfers the state from the busy state B1to an idle state I2. Further, the counter setting unit 7 of thetransmission control unit 20 sets the initial value in the counter 3 sothat the counter 3 starts decrementing of the count value.

At a certain time (t4), when the state determination unit 6 of thecarrier sense unit 2 transfers the state from the idle state I2 to abusy state B2 indicating that the transmission medium is in use, thecounter setting unit 7 of the transmission control unit 20 thereof setsthe initial value in the counter 3.

When the state determination unit 6 of the carrier sense unit 2transfers the state from the busy state B2 to an idle state I3 (t5), thecounter 3 starts decrementing of the count value.

At a certain time (t6) of the FIG. 2, processing determining whether thetransmission medium is in use or free is occurred because of a triggercondition is satisfied. For example, when the strength of a radio wavebecomes equal to or more than the predetermined threshold or the radiowave of a predetermined waveform is detected, it is determined that thetrigger condition is satisfied.

According to the conventional carrier sense function, the pending stateof this embodiment is not applied. In the conventional carrier sensefunction, when determination processing which determined that whether ornot the transmission medium is in use is occurred, “the idle state I3 ismaintained and the decrementing of the count value of the counter ismaintained” or “the state transfers from the idle state I3 to the busystate and the initial value is set in the counter” is carried out. Whenthe idle state I3 is maintained and the decrementing of count value ofthe counter is maintained, a frame transmission S1 is possible at thetime (t7) the count becomes zero. However, there is a problem that acollision occurs when the transmission medium is being used in adetermination result. When the state transfers from the idle state I3 tothe busy state and the initial value is set in the counter, thedecrementing of the count value of the counter is started from the time(t8) the state transfers from the busy state to the idle state. Thetransmission is stopped during the decrementing, and then, transmissionS2 of a transmission frame is possible at the time (t9) the count valuebecomes zero. In this case, the transmission of the transmission frameis delayed.

In contrast, according to this embodiment, the state determination unit6 of the carrier sense unit 2 transfers the state from the idle state I3to a pending state P1 at a time that “determination processing whichdetermines whether a transmission medium is in use or free” occurs.

In the pending state P1, the counter 3 continues decrementing becausethe state is not in the busy state indicating that the transmissionmedium is being used. Conversely, the transmission determination unit 8of the transmission control unit 20 prohibits the frame transmissionbecause of a possibility of using the transmission medium in the pendingstate P1 is relatively higher than the case of the idle state.

According to this embodiment, when the transmission determination unit 8of the transmission control unit 20 determines that the state is thepending state P1, even if the count value of the counter 3 becomes zero(t7), the transmission determination unit 8 of the transmission controlunit 20 does not permit a transmission immediately. In this way, it ispossible to prevent an occurrence of transmission collision.

The use determination unit 5 of the carrier sense unit 2 determineswhether the transmission medium is in use or free. As a result, when itis determined that the transmission medium is free, the statedetermination unit 6 of the carrier sense unit 2 transfers the statefrom the pending state P1 to an idle state I4. If the state is the idlestate I4 and the count value is zero, the state determination unit 6 ofthe carrier sense unit 2 permits a frame transmission S3. Therefore, thetransmission frame is transmittable earlier than the case of nothandling the pending state.

According to the foregoing embodiment, a data transmission collision isavoided, and further, a transmission opportunity is earlier obtained.Therefore, the communication device of this embodiment is especiallyeffective in the use under the condition that the determinationprocessing that whether a transmission medium is in use or freefrequently occurs.

Second Embodiment

The second embodiment explains the configuration of a communicationdevice, which performs a state transition for any of a busy state, apending state and an idle sate based on a received signal.

FIG. 3 is a block diagram indicating an example of the configuration ofa communication device according to a second embodiment.

A communication device 9 includes a receiving signal strength measuringunit 10, a threshold determination unit 11, a receiving trigger unit 12,a preamble detector 13, a receiver 14, a carrier sense unit 15 and atransmitter 16.

The receiving signal strength measuring unit 10 inputs a received signal201, measures a received signal strength, and then, outputs a measuredresult to the threshold determination unit 11.

The threshold determination unit 11 compares a predetermined thresholdwith the measured result supplied from the received signal strengthmeasuring unit 10, and then, outputs a comparison result to the carriersense unit 15.

The received trigger unit 12 issues a frame receiving start signal basedon the received signal 201 to output the frame receiving start signal tothe carrier sense unit 15 and the receiver 14. More specifically, forexample, when a significant rise of a received signal power is detected,a predetermined cycle in the received signal is detected, or acorrespondence of the received signal and a predetermined waveform isdetected, the receiving trigger unit 12 issues a frame receiving startsignal. In addition, a signal header detection processing disclosed inJpn. Pat. Appln. KOKAI Publication No. 2004-104499 may be used.Moreover, for example, the receiving trigger unit 12 issues the framereceiving start signal based on a signal received in the past at time areceived frame arrival is expected.

The receiver 14 demodulates and decodes the received signal after theframe receiving start signal is inputted. After a frame receiving iscompleted, the receiver 14 outputs a frame receiving end signal to thecarrier sense unit 15.

The preamble detector 13 analyzes the received signal 201 when inputtinga frame receiving start signal from the receiving trigger unit 12.Specifically, the preamble detector 13 determines whether a header ofthe received signal 201 has a predetermined waveform, and then, outputsa determined result to the carrier sense unit 15.

The carrier sense unit 15 inputs each signal from the thresholddetermination unit 11, receiving trigger unit 12, preamble detector 13and receiver 14, and determines whether or not transmission is possibleaccording to a predetermined rule such as the IEEE 802.11 standard.

The transmitter 16 transmits a transmission frame when the transmissionframe is prepared and the carrier sense unit 15 determines that thetransmission is possible.

FIG. 4 is a view to explain an example of a state transition of thecarrier sense unit 15 according to this embodiment.

As described above, the busy state is a state indicating that thetransmission medium is in use. The pending state is a state indicatingthat whether or not the transmission is in use is being determined. Theidle state is a state indicating that the transmission medium is free.

A transition from the idle state to other states will be describedbelow.

A second carrier sense unit 15 b of the carrier sense unit 15 transfersthe state from the idle state to the busy state when (A) the outputtedsignal from the threshold determination unit 11 indicating that thereceived signal strength is equal to or more than the predeterminedthreshold in the idle state.

The second carrier sense unit 15 b of the carrier sense unit 15transfers the state from the idle state to the pending state when (B)the receiving trigger unit 12 issues the frame receiving start signal(frame receiving start) in the idle state.

When (A) the received signal strength is equal to or more than thepredetermined threshold and (B) the receiving trigger unit 12 issues theframe receiving start signal in the idle state, the second carrier senseunit 15 b of the carrier sense unit 15 transfers the state from the idlestate to the busy state to preferentially select the (A).

A transition from the pending state to other states will be describedbelow.

A third carrier sense unit 15 c of the carrier sense unit 15 transfersthe state from the pending to the busy state in the case of (C) that thethird carrier sense unit 15 c inputs a signal indicating that the headerof the received signal from the preamble detector 13 has thepredetermined waveform (the header is preamble) in the pending state.

The third carrier sense unit 15 c of the carrier sense unit 15 transfersthe state from the pending state to the busy state in the case of (D)that the third carrier sense unit 15 c inputs a signal indicating thatthe header of the received signal from the preamble detector 13 does nothave the predetermined waveform (the header is not preamble) in thepending state.

The third carrier sense unit 15 c of the carrier sense unit 15 transfersthe state from the pending state to the busy state in the case of (E)that the threshold determination unit 11 determines that the receivedsignal strength is equal to or more than the predetermined threshold inthe third state.

When (E) the received signal strength is equal to or more than thepredetermined threshold and (D) the second carrier sense unit 15 binputs a signal indicating that the header of the received signal fromthe preamble detector 13 does not have the predetermined waveform (theheader is not preamble) in the pending state, the third carrier senseunit 15 c of the carrier sense unit 15 transfers the state from thepending state to the busy state to preferentially select the (E).

A transition from the busy state to other states will be describedbelow.

A first carrier sense unit 15 a of the carrier sense unit 15 stays inthe busy state in the case of (F) that a frame is being received in thebusy state. For example, the carrier sense unit 15 determines whether ornot the frame is in receiving (the frame is being received) based on theframe receiving start signal being issued by the receiving trigger unitand the frame receiving end signal being issued by the receiver.

The first carrier sense unit 15 a of the carrier sense unit 15 transfersthe state from the busy state to the idle state when (G) the outputtedsignal from the threshold determination unit 11 indicating that thereceived signal strength is not equal to or more than the predeterminedthreshold in the busy state.

When (F) the frame is being received and (G) the received signalstrength is not equal to or more than the predetermined threshold in thebusy state, the first carrier sense unit 15 a of the carrier sense unit15 stays in the busy state to preferentially select the (F).

A transition condition transferring from the busy state to the pendingstate may be added in this embodiment.

As described above, state transitions of the carrier sense unit 15 iscontrolled, and thereby, the following advantage is obtained.Specifically, if the receiving trigger unit 12 issues the framereceiving start signal in error, that is, actually, even if a frame doesnot arrive; nevertheless, the frame receiving start signal is issued,the state does not transfer to the busy state. Therefore, this serves toreduce a loss of a transmission opportunity.

The foregoing functions of the communication devices according to theembodiments can be realized by both of software and hardware.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A communication device comprising: a first unit determining thatwhether a state is a first state indicating that a transmission mediumis in use, a second state indicating that the transmission medium is notin use, or a third state indicating that whether or not the transmissionmedium is in use is being determined; and a second unit prohibiting adata transmission in the first and third states, and permitting the datatransmission in the second state, wherein the first unit comprises: afirst determination unit determining that the transmission medium is inuse or not; and a second determination unit determining that the stateis in the first state when the first determination unit determines thatthe transmission medium is in use, determining that the state is in thesecond state when the first determination unit determines that thetransmission medium is not in use, and determining that the state is inthe third state when the first determination unit determines thatwhether or not the transmission medium is in use is being determined,and the second unit comprises: a counter incrementing or decrementing ahold value; a counter setting unit setting a count value of the counteras a predetermined value when the second determination unit determinesthat the state is in the first state, starting incrementing ordecrementing of the count value when the state transfers from the firststate to the second state, and maintaining an operation of incrementingor decrementing of the counter value of the counter when the statetransfers from the second state to the third state; and a thirddetermination unit determining that the data transmission is possiblewhen the second determination unit determines that the state is in thesecond state and the counter value of the counter is equal to or morethan or equal to or less than a threshold value.
 2. The device accordingto claim 1, conforming to an IEEE 802.11 standard.
 3. The deviceaccording to claim 1, further comprising: a unit performing the datatransmission when the third determination unit determines that the datatransmission is possible.
 4. A communication method comprising:determining that whether a state is a first state indicating that atransmission medium is in use, a second state indicating that thetransmission medium is not in use, or a third state indicating thatwhether or not the transmission medium is in use is being determined;and prohibiting a data transmission in the first and third states, andpermitting the data transmission in the second state, wherein thedetermining comprises: determining whether or not the transmissionmedium is in use; and determining that the state is in the first statewhen it is determined that the transmission medium is in use,determining that the state is in the second state when it is determinedthat the transmission medium is not in use, and determining that thestate is in the third state when it is determined that whether or notthe transmission medium is in use is being determined, and theprohibiting and permitting comprises: setting a count value of a counteras a predetermined value when it is determined that the state is in thefirst state, starting incrementing or decrementing of the count valuewhen the state transfers from the first state to the second state, andmaintaining an operation of incrementing or decrementing of the countervalue of the counter when the state transfers from the second state tothe third state; and determining that the data transmission is possiblewhen it is determined that the state is in the second state and thecounter value of the counter is equal to or more than or equal to orless than a threshold value.
 5. The method according to claim 4,conforming to an IEEE 802.11 standard.
 6. The method according to claim4, further comprising: performing the data transmission when the datatransmission is possible.